The neurotrophins are a family of structurally and functionally related proteins, including Nerve Growth Factor (NGF), Brain-Derived Neurotrophic Factor (BDNF), Neurotrophin-3 (NT-3), Neurotrophin-4/5 (NT-4/5) and Neurotrophin-6 (NT-6). These proteins promote the survival and differentiation of diverse neuronal populations in both the peripheral and central nervous systems (Hefti, 1986; Hefti and Weiner, 1986; Levi-Montalcini, 1987; Barde, 1989; Leibrock et al., 1989; Maisonpierre et al., 1990; Rosenthal et al., 1990; Hohn et al., 1990; Gotz et al., 1994; Maness et al., 1994) and are involved in the pathogenesis of diverse neurological disorders. Neurotrophins exert many of their biological effects through specific interactions with a class of transmembrane receptor tyrosine kinases (trkA, trkB and trkC) (Kaplan et al., 1991; Klein et al., 1991, 1992; Soppet et al., 1991; Squinto et al., 1991; Berkemeier et al., 1991; Escandon et al., 1993; Lamballe et al., 1991). Specificity of neurotrophin action results from their selective interactions with the trk receptors. That is, trkA only binds NGF (Kaplan et al., 1991; Klein et al., 1991); trkB binds BDNF and NT-4/5 (Soppet et al., 1991; Squinto et al., 1991; Berkemeier et al., 1991; Escandon et al., 1993; Lamballe et al., 1991; Klein et al., 1992; Vale and Shooter, 1985; Barbacid, 1993); and trkC exclusively binds NT-3 (Lamballe et al., 1991; Vale and Shooter, 1985). This is particularly evident when the trk receptors are coexpressed with the common neurotrophin receptor p75NTR. (For review see Meakin and Shooter, 1992; Barbacid, 1993; Chao, 1994; Bradshaw et al., 1994; Ibáñez, 1995).
The common neurotrophin receptor p75NTR is a transmembrane glycoprotein structurally related to the tumor necrosis factor and CD-40 receptors (Meakin and Shooter, 1992; Rydén and Ibáñez, 1996). As all neurotrophins bind to p75NTR with similar affinity (Rodriguez-Tébar et al., 1990; Hallböök et al., 1991; Rodriguez-Tébar et al., 1992; Ibáñez, 1995), neurotrophin specificity is conventionally thought to be caused by the binding selectivity for trk receptors which are differentially expressed in different neuronal populations (Ibáñez, 1995). However, accumulated experimental data on neurotrophin activity reveal important functional aspects of p75NTR (Heldin et al., 1989; Jing et al., 1992; Herrmann, 1993; Barker and Shooter, 1994; Dobrowsky et al., 1994, Matsumoto et al., 1995; Marchetti et al., 1996; Washiyama et al., 1996). The common neurotrophin receptor enhances functions and increases binding specificity of trk receptors (Barker and Shooter, 1994; Mahadeo et al., 1994; Chao and Hempstead, 1995; Rydén and Ibáñez, 1996). In addition, p75NTR possesses unique, trk-independent signaling properties which involve ceramide production through activation of the sphingomyelin cycle (Dobrowsky et al., 1994), apoptosis (cell death) (Van der Zee et al., 1996; Cassacia-Bonnefil et al., 1996; Frade et al., 1996), and activation of the transcription factor NFκB (Carter et al., 1996). Recently, p75NTR has been demonstrated to participate in human melanoma progression (Herrmann et al., 1993; Marchetti et al., 1996). Furthermore, NGF and NT-3 increase the production of heparin by 70 W melanoma cells, which is associated with their metastatic potential (Marchetti et al., 1996). Although this effect has been shown to be mediated by the common neurotrophin receptor, neither BDNF nor NT-4/5 appeared to be active.
Due to the implication of NGF/p75NTR binding in various disease states, a need exists for pharmaceutical agents and methods of use thereof for interfering with the binding of NGF to the p75NTR common neurotrophin receptor.